The Qualcomm-backed start-up's claim to fame is its tiny electrocardiogram, which tucks into a custom Apple Watch band and screens for atrial fibrillation, a leading cause of strokes. It also recruited a prominent CEO in Vic Gundotra, the former senior vice president of engineering at Google.

Earlier this week, it reached a big milestone when the Food and Drug Administration gave it "breakthrough device designation" to use its EKG to screen for elevated potassium levels without requiring any blood.

On Wednesday, the company announced that it had developed its own EKG for the Apple Watch, potentially replacing the AliveCor one. And its EKG sensor and apps had clearance from the FDA to provide consumers with access to their EKG readings immediately (in AliveCor's case, a doctor reviews it for free within 24 hours to unlock the first reading).

But Gundotra told CNBC that Apple gave his start-up its biggest boost yet.

Before Apple spoke about it on stage, Gundotra said many people had never even heard of an EKG, let alone bought one. In the wake of Apple's event, he said, AliveCor has seen a doubling in traffic to its website and an 80 percent jump in sales for its portable EKGs.

It's possible that AliveCor, which is backed by more than $40 million in venture capital, could take a bigger hit when Apple launches the EKG and its mobile apps later this year. But for now, Gundotra says, the company is profiting from the attention. He also makes the case that his company's devices are available for just $99 and up, while the Series 4 of the Apple Watch starts at $399.